Electronic selector switch



Sept. 10, 1957 s. HANSEN 2,806,175

ELECTRONIC SELECTOR SWITCH :Filed May 1o, 1954 2 sheets-sheet 1 Sept. 10, 1957 s. HANSEN ELECTRONIC SELECTOR SWITCH 2 Sheets-Sheet 2 Filed May l0, 1954 Unite ELECTRONIC SELECTOR SWITCH Application May 10, 1954, Serial No. 428,762

4 Claims. (Cl. 315-12) This invention relates to an electronic switching device and more particularly to an electronic switching system incorporating a cathode ray device.

The employment of digital computers in control systems often requires that separate and successive readings be taken from a plurality of instruments. These readings are normally derived in the form of direct-current voltages, the magnitudes of which are proportional to indicated or measured instrumentally recorded quantities. In the operation of the system it is necessary that these voltages, called input voltages, be sampled according to a predetermined arrangement and repeatedly and successively read by selector switches which are connected to a common output terminal.

It has been the practice to employ mechanical commutator or rotary switches to perform computer switching functions. In some cases, mechanical switches are unsatisfactory because of their relatively short lives. In `a great many cases, the maximum operating speed of these switches is so slow that they are made completely useless for some computer applications. In this event, electronic circuits are employed to replace the mechanical switches. These circuits normally include numerous conventional electron tubes. In View of the number of tubes required to perform a relatively few switching functions, the original cost, the maintenance costs, and the operating power loss, the cost of operating these circuits is unfavorably high. Frequently, the space necessarily occupied by this type of equipment is also an outstanding disadvantage.

Cathode ray type electron tubes are sometimes employed to perform various non-computer switching functions. These tubes normally comprise a conventional electron gun for producing an electron stream, stream deilector plates, sweep voltage sources for deecting the stream, and a plurality of target electrodes, commonly called targets, from which separate output signals are taken. Currently, these cathode ray tubes are only employed as output devices having single inputs and multiple outputs connected to the targets. In particular, cathode ray devices are not presently employed as digital computer input switches because it is necessary to prevent loading the input sources which are connected to the targets.

By practicing the present invention, digital computer input switching may be accomplished by the use of a cathode ray device of the general type described wherein means are provided for sampling input signal amplitudes and for producing them at a single output terminal with no substantial loading of the input sources.

Multiple electronic switching is accomplished with the present invention by means of a cathode ray device including an electron gun for producing an electron stream, stream deflection means, a plurality of target electrodes, and a collector electrode. The targets, which are each responsive to an input signal to be sampled, are constituted of secondary electron emissive materials. The collector electrode has the form of a metallic multicellular structure which substantially encloses each separate target so as to isolate it from the others.

States Patent Cil ICC

In its operation, the particular target responsive to the input signal to be sampled is bombarded by the electron beam which is intensity modulated with an alternatingcurrent voltage of a predetermined frequency. The bombardment by the electron beam causes a current to flow either to or from the target, depending on whether the potential of the target is greater or less than the potential of the collector electrode. In the case where the potential of the target is substantially the same as that of the -collector electrode, no current flows. When a current does ow, however, the current flowing to and the current flowing from the target each contain alternatingcurrent components that are opposite in phase and are of a magnitude proportional to the total current flowing. The alternating-current component in the current flowing to or from the target is amplified by an alternating-current amplifier and compared to the original alternatingcurrent voltage of predetermined frequency by a phase detector to produce a direct current potential of an amplitude and polarity dependent on the amplitude and phase of the alternating-current component. This directcurrent potential is integrated by means of a high-gain direct-current amplifier and the resulting output signal impressed on the collector grid in a manner to minimize the diiference in its potential from that of the target element. Thus, the output signal developed at the output terminal of the high-gain direct-current amplifier by virtue of its connection to the collector electrode, is substantially an exact reproduction of the input signal impressed on the particular target being bombarded by the electron bearn. It is thus seen that the target, collector electrode, alternating-current amplier, phase detector, and high-gain direct-current amplifier form what may be designated as a high-gain null-seeking closed servo loop. Also, in order to switch to a particular input signal, it is only necessary to deect the electron beam to the appropriate target.

t is therefore an advantage of the present invention in that it may be employed to accomplish input switching in a more rapid manner than heretofore practiced in taking data in digital computer applications. For example, sampling time may be easily reduced to or 200 microseconds. The invention has a greater life span than high speed mechanical switches; however, unlike conventional electronic switching circuits, the original cost and maintenance of the present invention is very low compared to its relative utility. For example, one cathode ray tube with associated circuitry, constructed in accordance with the invention, may replace fifty to one hundred conventional tubes in electronic switching circuits presently en ployed.

It is an object of the invention to provide an improved cathode ray electronic switching device.

lt is another object of the invention to provide a cathode ray electronic switching device for sampling the voltage of a selected complex wave source without substantially loading the source.

The novel features which are believed to be characteristic ofthe invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawing in which an embodiment of the invention is illustrated by way of example. lt is to be cxpressly understood, however, that the drawing is for the purpose of illustration and description only, and is not intended as a definition of the limits of the invention.

Fig. l is a schematic diagram of an embodiment of the tube and circuit of the present invention; and

Figs. 2 5 are waveforms explanatory of the operation of the device of Fig. 1.

Referring now to Fig. l there is Villustrated an empleting the closed servo feedback loop formed by the target 160, the alternating-current amplifier 12, the phase detector 14, and the integrator circuit 16 which includes high-gain direct-current amplier 130.

In its operation the modulated electron beam is directed by target selecting circuit 18 to a target element of target assembly 38 that `is responsive to the particular input signal that it is desired to switch to the output terminals 24. Bombardment of this one of the target elements 19t] produces a secondary electron emission characteristic 149 as illustrated in Fig. 2. In this figure, the current from a bombarded target element per unit of beam current is plotted versus the cathode-totarget potential. As -is apparent from this characteristic, the electrons of the beam initially strike the target at such a low potential that few true secondary Ielectrons are produced. The target element intercepts the beam current, however, which results in a negative current thereto. As the electrons of the beam bombard the target element at higher and higher voltages an increasing number of secondary electrons are produced until a point is reached where the number of secondary electrons is equal to the number of primary electrons Iimpinging o-n the element.

The voltage through which the electrons have been accelerated at this point is generally designated as the critical voltage, Vo, of the secondary electron emissive surface of the target element.

As the electrons of the beam strike the target element at increasingly higher velocities greater than this critical voltage, the number of secondary electrons becomes increasingly greater than the primary electrons incident on the target element. If the velocity of the incident primary electrons is increased still further, they penetrate deeper into the molecular matrix comprising the target element until the point is reached where increasingly greater numbers of the prospective secondary `electrons cannot get free of the surface and hence result in a decrease in the number of secondary electrons. In the case that the secondary electrons are collected at a particular potential, Va, the secondary electrons obviously cannot be collected at potentials substantially greater than this. Hence the current from a bombarded target element will decrease in the manner indicated by the line portion 142. An increase or decrease in the potential of the collector electrode 102 `would obviously cause the bombarded target element to tend to charge towards this potential.

This phenomenon is employed in the present invention to reproduce an input signal on the output terminals. Thus, with an initial collector voltage Vc, and a target element at a potential Va, as shown in Fig. 2, a positive current would flow from the bombarded target element. if the electron beam were modulated, this current flowing from the target element would obviously be greater for the larger values of beam current and smaller for the smaller values and, thus, would vary sinusoidally in the same manner and same phase as the reference signal. This is shown in Fig. 3 as voltage waveform 150. On the other hand, with the collector electrode potential still at Vc, if the target electrode were at a potential such as Vb as shown in Fig. 2, a negative current would flow from the bombarded target element. This negative current would also increase and `decrease in magnitude with the beam current and thus vary sinusoidally in the same manner. This is shown as waveform 152 in Fig. 3. It is noted that in comparing waveforms 150 and 152 that the positive current is 180 different in phase than the negative current. Further, the amplitude of the alternating component of the current in each case is proportional to quiescent current from the target element bombarded by the electron beam. Thus if a target element is charged to the point where the same number of secondary electrons leave the target element as are incident thereon, no further change in potential will take place. This poF tential will normally be only a few volts higher than the collector electrode potential. As illustrated in Fig. 2,

if the collector electrode 102 were at the potential Ve, the target element would charge to a potential corresponding to a point 144 on the secondary electron emission charge characteristic.

In the operation of the electronic switching circuit of the present invention, the electron beam, as previously mentioned, is caused to bombard a target element that is responsive to a particular signal that it is desired to switch to the output terminals 24. If the instantaneous voltage of this target element is below or above that of the collector electrode 102, a positive or a negative current, respectively, will ow from the target element due to secondary electron emission. Modulation of the electron beam will cause this current to vary sinusoidally in magnitude. Variable capacitor is adjusted so that the alternating current component of the current from the bombarded target element has a maximum amplitude at the input terminals of alternating current amplifier 12. The magnitude of this current is indicative of the error between the potential of the collector electrode 102 and that of the target element 100.

Amplilier 12 amplies this `alternating current error component and impresses it across the primary winding 114 of transformer 112 of the phase detector 1,4. A corresponding current is induced in the secondary Winding 116 of transformer 112 which impresses potentials of opposite phase relation on the plate of diode 118 and on the cathode of diode 120. Figs. 4 and 5 illustrate, respectively, the voltages appearing across diodes 118 and 120. Waveform in Fig. 4 and waveform 162 in Fig. 5 show the manner in which the error voltage appears across diodes 118 and 12), respectively. The reference signal, on the other hand, is applied -to the center tap 117 of secondary winding 116 so that it appears in phase on both diodes. This is shown as waveform 164, Fig. 4, and waveform 166, Fig. 5, for the respective diodes. In the case of diode 118` the two voltages will add numerically, thus providing a signal represented as waveform 168, Fig. 4 which has an amplitude that is larger than the reference signal alone. In the case of diode 120, however, the error and reference voltages are of opposite phase and hence will subtract whereby the resulting voltage, shown as waveform 170, Fig. 5, is of a smaller amplitude than the reference signal. The two resultant signals 163, 175 are rectified and tend to charge capacitor 126 through resistors 122 and 124, respectively. The shaded areas beneath the waveforms 168, indicate the periods and the relative conduction of the diodes 118, 120, respectively. From examination of these areas, it is apparent that a resultant charge is produced on capacitor 126 only when `there is a difference in amplitude of the two signals. This resultant voltage is designated as a direct-current error signal voltage. r

This direct-current error signal voltage is integrated by the circuit 16 in such a manner that the voltage appearing at output terminals 24, which is connected to the collector electrode 102, is changed in a direction toward the point of zero charging current from the target element. For example, referring to Fig. 2, if the initial potential of the target element were Va, the error signal thus produced would be integrated in such a manner so as to decrease the potential of the collector electrode 102 until it were equal `to Vc. If the initial potential of the target element were Vb, the error signal would be of opposite phase and hence would increase in the opposite direction and increase the potential of the collector electrode 102 until it were equal to Vc. Thus, as is evident from this diagram, the potential of the output circuit is always substantially equal to the input signal impressed upon the particular target element being bombarded by the electron beam.

From the above, it is evident `that a high-gain null-` seeking servo loop is formed by the alternating-current ':1n3plfi-te1::12Kcoupled toathe targetelements 10.0,-the p hase detector,l4 responsive .t-ofthe :output from -ampliiier `12 andthetvoltageof predeterrrlined frequency used to moduf late the electron beam to produce a direct-current .error t signal,,andiitherintegratorAcircui-t 16 for integratingthe errorgisignaltogproducea potential which is impressed .0n tthevcollector elect-rode 102 ,and which, 1in addition, servesgas lan outputfsignal.

-fwhaty fis= ,claimed is 1.Anelectronic :switchingl device for selectively reproduci `fany oneofazplurality ,ofJinputfsignala s aid de- :vice: omprisinga plurality of secondary electron yemis- V sive; argetticlementaleachtof said :target lelementsbeing re'spansive:toroneiofzsaidv input gsignals, :means for .p1-.o-

, an electrn fstream, 4a source capable of -providngz'a reference; signal offpredetermined frequency, means forizmcrdulating said electron '.streamwith :said reference sgnaL-zmea-ns 'for directing said :modulated electron. stream towardssasselectedltarget. element responsive to an input Vsignale-desired to'ibe reproduced,-wl1ence secondary electrons are emitted from `said =targetelement, a collector electrode for lcollecting Vsaid Asecondaryelectrons whereby kan error current flows from .said selected target element, `and fmeans coupled to said reference signal sour-cetandsaidv target -elernentf and -having an outputcon- -nected' to -said collector electrode for lgenerating :ane-output voltagecn said collector Velectrode capable of-rle'- creasingsaid` error current to zerorfwherebysaid output voltage :is substantially equal to said input: signal Ldesired Itor-:be reproduced.

` 2.\Theelectronicswitching device vas denedinclaim 1-.vvhereinsaid `means coupled to-said Vreferencesignal source andfsaid target element comprises-a phase detector `responsive to thephase of saidwrference signal -and=the phase and. amplitude `of said error current lto produce a direct-currentpotentalhaving polarity andmagnitude idependent upon the phaseand amplitude, respectively,of

said error cu1-rent,y and `means ,coupled vto saidy phasefdetectorian'd responsive -to said direct-current'potential for generating said output voltage. Y Y

13. t-"lfhenrele,ct'ronicgsvvitchirigf` device as .delned in claim Secondary electrons from lfsaid target-elements, Van electronagun-Qapable -Qf`producing anrelec'tron stream, means for directing-said electron stream towards'a selected target-#lement responsive-toaninput signal desired to be reproduced, wand, apparatus for vproducing an output-101tagerepreselntativeiof gsaid' input signal'desired tobe reprodueed; s a apparatus-comprising jasource providing a reference 1. t Y towsaidgelect'ron gung fortmodulating said electronl stream, whereby :an errorzsignalfcurrent of' a frequency4 equal to saidepredeterminedfrequency flows from said selected t targetg-elelr'ient,l said -errorsignalhaving a magnitude andV phasesfdependent onthe Vdierence in potentialbetweenrV Y saidtselected'targetelement land;said collector electrode,Y andameansacoupledtto said lreference signal sourcevandV said.A target elementfandfhaving an :output Vconnected to saidecollectorelectrodefor changing the magnitude ofV saiddierencezi-n p otentialfin.a:manner to-decrease said error current to zero Wherebythe voltage available at said-output Lis representativegof said input` signalldesired tohlaereproduced.V Y v u'Refer'encesGitediny Vthe file -ofthis patent Y Y p YrnsurEDsfrA'rEs PATENTSl 2,520,170

-zIRanson Aug. l29, 1950 2;5427;l;l3 :Anderson a Oct. 2.4, 1950 12,607,903 rLabin Aug-19, 1952 Mortoniet: al. Nov. 10,'1953 gnal of predetermined 4frequency Vcoupled' 

